Scientists have yet to discover, or classify, about 90 percent of the plant and animal species on Earth, which is estimated to be home to just under 9 million species, a study says. The study, published in the open-access journal PLoS Biology on Wednesday, vastly increases the estimated richness of life on the planet. More than 1.2 million species have been formally described and named so far. Scientists have long tried to classify life on Earth and to finally figure out how many species there are but estimates have varied wildly from 3 million to 100 million.